Process for producing a high quality lube oil stock

ABSTRACT

A waxy hydrocarbon feedstock is converted into a high quality lube oil stock of reduced pour point by hydrodewaxing the feedstock in the presence of molecular hydrogen and a hydrodewaxing catalyst under conditions such that the pour point of the feedstock is reduced by selectively converting waxy paraffins into lower molecular weight hydrocarbons. At least a portion of the effluent from the hydrodewaxing zone is then passed to a hydrocracking zone where it is contacted with a hydrocracking catalyst under conditions such that a further reduction in pour point is effected and the overall conversion of components boiling above about 650° F. to components boiling at or below about 650° F. in the hydrodewaxing and hydrocracking steps combined is no more than about 20 percent by volume, preferably no more than about 10 percent by volume.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.593,439, filed in the U.S. Patent and Trademark Office on Mar. 26, 1984and now U.S. Pat. No. 4,648,958, which is a continuation-in-part of U.S.patent application Ser. No. 531,924, filed in the U.S. Patent andTrademark Office on Sept. 13, 1983 and now U.S. Pat. No. 4,517,074,which is a divisional of U.S. patent application Ser. No. 084,761 filedin the U.S. Patent and Trademark Office on Oct. 15, 1979 and now U.S.Pat. No. 4,419,271.

BACKGROUND OF THE INVENTION

This invention relates to a process for converting a waxy hydrocarbonfeedstock into a high quality lube oil stock. It is particularlyconcerned with a process for producing a high quality lube oil stockhaving a relatively low pour point from a full boiling range shale oil.

Many hydrocarbon liquid feedstocks contain relatively highconcentrations of straight chain and slightly branched aliphaticcompounds having between 8 and 40 carbon atoms. These long chaincompounds tend to crystallize on cooling of the hydrocarbon oil. Thiscrystallization is quite frequently sufficient to hinder the flow of thehydrocarbon liquid and prevent it from being pumped or transmitted fromone location to another. The temperature at which the hydrocarbon oilwill not flow is commonly referred to as the "pour point" and isdetermined by standardized test procedures. One such feedstock having arelatively high pour point is the raw oil obtained by retorting oilshale, such as the oil shale found in the Colorado River formation inthe western United States.

Oil shale is a mixture of a minor amount of solid organic matter knownas kerogen and a major amount of mineral matter. Hydrocarbons arenormally recovered from oil shale by subjecting it to heat via pyrolysisor retorting at temperatures between about 850° F. and about 1000° F.These high temperatures cause the kerogen to decompose into liquid andlight gaseous hydrocarbonaceous products. The liquids recovered bycondensing the oil shale vapors will normally contain a relatively highconcentration of straight chain and slightly branched paraffins of highmolecular weight. This high concentration of waxy components typicallyresults in the oil having a relatively high pour point, normally betweenabout 50° F. and about 90° F. In addition, the raw shale oil willcontain arsenic, organonitrogen constituents and/or organosulfurconstituents.

U.S. Pat. No. 4,153,540 teaches a method of upgrading raw shale oil byremoving the organonitrogen and organosulfur compounds and also reducingthe pour point. The shale oil is treated in a two-step process in whichthe shale oil is first contacted with a hydrotreating catalyst underconditions such that the concentration of organosulfur andorganonitrogen constituents is reduced. The hydrotreated shale oil isthen contacted with a hydrodewaxing catalyst under hydrodewaxingconditions in the presence of molecular hydrogen such that the feedstockis hydrodewaxed while its 750° F. + boiling fraction is converted by atleast 50 percent to products boiling below 750° F. The hydrodewaxingcatalyst utilized comprises a ZSM-5 zeolite in its hydrogen formcombined with a metal having activity for promotinghydrogenation/dehydrogenation reactions. The use of ZSM-5 and relatedporous, crystalline aluminosilicates results in the conversion of thestraight chain and slightly branched paraffins into lower boilingcomponents, thereby decreasing the pour point of the treated oil.

The process described in U.S. Pat. No. 4,153,540 has a seriousdisadvantage if it is desired to convert the raw shale oil into a lubeoil stock of relatively low pour point. Since lube oil stocks normallyboil between about 650° F. and about 1000° F., it is undesirable intreating the shale oil to convert a large portion of its higher boilingconstituents to lower molecular weight constituents which boil in thegasoline range. It appears, however, that the hydrodewaxing stepdisclosed in the process of U.S. Pat. No. 4,153,540 is quitenonselective in that not only are waxy paraffins hydrocracked to lowerthe pour point but 50 percent or more of the 750° F. + constituents arecracked as well. Such excess hydrocracking results in substantial yieldlosses when the desired product is a high quality lube oil stock havinga relatively low pour point.

In order to avoid excessive yield losses in the process disclosed inU.S. Pat. No. 4,153,540, the catalytic dewaxing step can be carried outwith the same catalyst at lower severity conditions. It has been found,however, that although significant yield losses are avoided by thistechnique, the pour point is not sufficiently decreased. Evidently,under more mild conditions, the catalyst is very selective to crackingof the straight chain paraffins while leaving a large proportion of theslightly branched paraffins in the oil.

Accordingly, it is one of the objects of the present invention toprovide a process for reducing the pour point of raw shale oil and otherwaxy hydrocarbon feedstocks without substantially decreasing the yieldof lube oil stock constituents boiling in the 650° F. + range. It isanother object to provide such a process having the further advantage ofselectively hydrocracking the straight chain and slightly branchedparaffins while not substantially hydrocracking other components.

SUMMARY OF THE INVENTION

In accordance with the invention, it has now been found that the pourpoint of waxy hydrocarbon feedstocks can be substantially decreasedwithout significant losses in lube oil stock constituents by contactingthe feedstock with a dewaxing catalyst in a dewaxing zone underconditions sufficient to reduce the pour point of the feedstock byconverting waxy paraffins into lower molecular weight hydrocarbons, andthen contacting the effluent from the dewaxing zone with molecularhydrogen in the presence of a hydrocracking catalyst under conditionssuch that a further reduction in pour point is effected. Normally, theoverall conversion of 650° F. + components to components boiling at orbelow about 650° F. in the dewaxing and the hydrocracking steps combinedis no more than about 20 percent by volume, preferably no more thanabout 10 percent by volume. A high quality lube stock having a reducedpour point is then recovered from the effluent of the hydrocrackingzone. Preferably, the waxy hydrocarbon feedstock is a dearsenated, rawshale oil that has been subjected to hydrotreatment to removeorganosulfur and organonitrogen compounds.

The dewaxing step of the invention is preferably accomplished underhydrodewaxing conditions. For purposes of the present invention, thedistinction between dewaxing conditions and hydrodewaxing conditions isthe presence of molecular hydrogen in the latter and the absence ofmolecular hydrogen in the former.

A preferred hydrodewaxing catalyst for use in the process of theinvention includes a Group VIB metal component and/or a Group VIII metalcomponent on a support comprising a mixture of a porous refractory oxideand a crystalline silica polymorph. A preferred hydrocracking catalystfor use in the process of the invention includes a Group VIB metalcomponent and/or a Group VIII metal component on a refractory oxidesupport comprising silica-alumina dispersed in a matrix of gammaalumina. The support may also contain an aluminosilicate zeolite havingcatalytic activity for cracking hydrocarbons. Normally, both thehydrodewaxing zone and the hydrocracking zone will be maintained at apressure between about 500 p.s.i.g. and about 2500 p.s.i.g. and at atemperature between about 500° F. and about 850° F.

The process of the invention provides a method for converting shale oiland other waxy hydrocarbon feedstocks into lube oil stocks havingsubstantially reduced pour points without excessive loss of lube oilboiling constituents. Thus, the process of the invention provides amethod for efficiently producing large quantities of high quality lubestocks from raw shale oil.

DETAILED DESCRIPTION OF THE INVENTION

Feedstocks for the process of the invention include waxy raffinates orwaxy distillates boiling above about 650° F., usually in the range fromabout 650° F. to about 1100° F. Such feedstocks, which often have pourpoints between about 70° F. and 90° F., may be treated in the process ofthe invention to produce lube stocks of low pour point, typically belowabout 10° F. The preferred feedstock is a full range shale oil or shaleoil fraction that has been deashed, dearsenated and catalyticallyhydrotreated. One method by which the dearsenation may be carried out isdescribed in U.S. Pat. No. 4,046,674, the disclosure of which is hereinincorporated by reference in its entirety. The hydrotreating step iscarried out by contacting the deashed and dearsenated shale oil withmolecular hydrogen in the presence of a hydrotreating catalyst, whichwill normally comprise Group VIB and Group VIII metal components on aporous refractory oxide support, under conventional hydrotreatingconditions in order to remove organosulfur and organonitrogen compoundsby converting them to hydrogen sulfide and ammonia, respectively. Whenshale oil derived by retorting oil shale found in the Colorado Riverformation and adjacent areas is subjected to the deashing, dearsenatingand hydrotreating in sequence, the shale oil produced will normally havea boiling point range between about 80° F. and about 1030° F., anorganonitrogen content of between about 200 wppm and about 3500 wppm,usually between about 300 wppm and 2000 wppm, an organosulfur contentbetween about 30 wppm and 2000 wppm, normally between about 35 wppm and100 wppm, and a pour point above about 70° F., normally between about75° F. and 90° F.

Typically, the hydrotreating step will be carried out at normalhydrogenation conditions in a conventional hydrotreating reactor inwhich the liquid feed is passed downwardly through a packed bed ofconventional hydrotreating catalyst. Such catalysts normally comprise analumina or silica-alumina support carrying one or more Group VIII metalsand one or more metals from Group VIB of the Periodic Table of Elementsin the form of an oxide or sulfide. Combinations of one or more GroupsVIB metal oxides or sulfides with one or more Group VIII metal oxides orsulfides are generally preferred. Normally, the preferred metalconstituents are either tungsten or molybdenum in combination witheither nickel or cobalt.

In accordance with the invention, the effluent from the hydrotreatingreactor is passed to a hydrodewaxing reactor where it is directeddownwardly through a bed of hydrodewaxing catalyst in the presence ofmolecular hydrogen at elevated temperature and pressure. Normally, thetemperature in the hydrodewaxing reactor will range between about 500°F. and about 850° F., preferably between about 600° F. and 800° F. Thepressure in the reactor will normally be between about 500 p.s.i.g. andabout 3,000 p.s.i.g., preferably between about 1,500 p.s.i.g. and about2,500 p.s.i.g. The rate at which the feedstock is passed through thereactor in contact with the catalyst particles is normally set at aliquid hourly space velocity between about 0.3 and about 8.0, preferablybetween about 0.5 and about 3.0. The hydrogen flow rate through thereactor is normally above about 5,000 standard cubic feet per barrel offeedstock, preferably between about 2,000 and about 8,000 standard cubicfeet per barrel.

The catalyst used in the hydrodewaxing reactor is a dewaxing catalystwhich, under the conditions in the reactor, is effective for reducingthe pour point of the feedstock by promoting the selective conversion ofwaxy paraffins, normally paraffins containing straight chains havingbetween about 8 and about 40 carbon atoms, to lower molecular weighthydrocarbons. One type of catalyst suitable for use as the hydrodewaxingcatalyst is composed of one or more Group VIB active metal components,particularly the Group VIB metals, oxides and sulfides, and/or one ormore Group VIII metal components, particularly Group VIII metals, oxidesand sulfides, on a support comprising an intimate mixture of a porousrefractory oxide and a crystalline silica molecular sieve essentiallyfree of aluminum and other Group IIIA metals. Normally, the metalsutilized will be nickel and/or cobalt constituents in combination withtungsten and/or molybdenum components. Nickel and tungsten components,especially in a sulfide form, are the most preferred metals for use inthis catalyst. The porous refractory oxides that can be used include theoxides of difficultly reducible metals, particularly those containingaluminum. Examples of such refractory oxides include alumina, silica,beryllia, chromia, zirconia, titania, magnesia, thoria and combinationsof these refractory oxides such as silica-alumina and silica-titania.The most preferred refractory oxides are alumina and gamma alumina. TheGroup IIIA metal-free crystalline silica molecular sieve which forms aportion of the support is preferably a material known as silicalite, asilica polymorph that may be prepared by methods described in U.S. Pat.No. 4,061,724, the disclosure of which is hereby incorporated byreference in its entirety. The resultant silicalite will preferably besubjected to combustion to remove organic materials and thenion-exchanged to eliminate traces of alkali metal ions. Silicalite doesnot share the zeolitic property of substantial ion exchange common tocrystalline aluminosilicates and therefore contains essentially nozeolitic metal cations. Unlike the "ZSM-5 family" of zeolites,silicalite is not an aluminosilicate and contains only trace proportionsof alumina. A more detailed description of the above-discussedhydrodewaxing catalyst including its method of preparation can be foundin U.S. Pat. No. 4,428,862, the disclosure of which is herebyincorporated by reference in its entirety.

Another catalyst which can be used in the hydrodewaxing reactor issomewhat similar to the catalyst described above except that acrystalline aluminosilicate of the ZSM-5 type, preferably in an acidicform, is substituted in the support for the crystalline silica molecularsieve essentially free of Group IIIA metals. The crystallinealuminosilicate zeolite will normally be present in the support as adispersion in the porous refractory oxide. The crystallinealuminosilicate zeolite may be ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35,ZSM-38 and the like. ZSM-5 is the most preferred and is fully describedin U.S. Pat. No. 3,702,886, the disclosure of which is herebyincorporated by reference in entirety. ZSM-11, ZSM-12, ZSM-23, ZSM-35,and ZSM-38 are all known zeolites and are more fully describedrespectively in the following U.S. patents, the disclosures of which arehereby incorporated by reference in their entirety: U.S. Pat. Nos.3,709,979; 3,832,449; 4,076,842; 4,016,245 and 4,046,859. These zeolitesare known to readily adsorb benzene and normal paraffins such asn-hexane and also certain mono-branched paraffins, such as isopentane,but have difficulty adsorbing di-branched paraffins, such as2,2-dimethylbutane, and polyalkylaromatics, such as meta-xylene. Thesezeolites are also known to have a crystal density of not less than 1.6grams per cubic centimeter, a silica-to-alumina ratio of at least 12,and a constraint index within the range of 1 to 12. The constraint indexis defined in U.S. Pat. No. 4,229,282, the disclosure of which is herebyincorporated by reference in its entirety. The foregoing zeolites havean effective pore diameter greater than 5 Angstroms with the poresdefined by 10 membered rings of oxygen atoms, as explained in U.S. Pat.No. 4,247,388, the disclosure of which is herein incorporated byreference in its entirety. Such zeolites are preferably utilized in theacid form by replacing at least some of the ion-exchanged metal cationsin the zeolite with hydrogen ions. This exchange may be accomplisheddirectly with an acid or indirectly by ion exchange with ammonium ionsfollowed by calcination to convert the ammonium ions to hydrogen ions.In either case, it is preferred that the exchange be such that asubstantial proportion of the ion exchange sites of the zeolite utilizedin the catalyst support is occupied with hydrogen ions. Normally, it isdesirable to remove any organic impurities from the zeolite bycombustion before the above-described ion exchange procedures arecarried out.

The support will normally consist essentially of an intimate mixture ofthe zeolite and a porous refractory oxide such as alumina. Theproportion of zeolite in the support may vary in the range between about2 percent and about 90 percent by weight, but preferably the supportconsists essentially of a heterogeneous dispersion of zeolite in amatrix of alumina or other porous refractory oxide. Such a dispersioncontains the zeolite in a minor proportion, normally between about 15percent and about 45 percent, preferably between about 20 percent andabout 40 percent by weight, with 30 percent being most highly preferred.

The hydrodewaxing catalyst is most preferably prepared in particulateform, with the clover-leaf form shown in FIGS. 8 and 8A of U.S. Pat. No.4,028,227, the disclosure of which is hereby incorporated by referencein its entirety, being most highly preferred. One convenient method forpreparing the catalyst involves first comulling a wetted mixture ofzeolite, an alumina gel, and an alumina binder material, such asCatapal® peptized alumina, in proportions appropriate to what is desiredin the final catalyst support. Such a comulled mixture is then extrudedthrough a die having suitable small openings in the shape of circles orellipses, or, as is preferred, three-leaf clovers. The extruded materialis cut into small particulates, dried, and calcined, following which theresulting support particles are impregnated with a liquid solutioncontaining the desired Group VIB element in dissolved form, with otheractive components, such as nickel, or even with an acidic component,such as phosphorus, known for its property to promote hydrotreatingreactions, being optionally included. A specifically contemplatedimpregnation liquid consists essentially of an aqueous solution ofdissolved ammonium metatungstate and nickel nitrate, with the dissolvedcomponents being present in the impregnation liquid in proportionssufficient to ensure that the final catalyst contains more than about 15percent by weight tungsten components calculated as WO₃ and more thanabout 0.5 percent by weight nickel components calculated as NiO. Ifdesired, phosphorus components may also be present in the impregnationliquid so that the final catalyst contains, for example, more than about0.5 percent by weight phosphorus components calculated as P. Afterimpregnation, the impregnated composite particles are calcined in air attemperatures at or above about 900° F. for a time period sufficient toconvert the metal components to oxide forms.

In an alternative method, the foregoing procedure is altered such that,instead of introducing the Group VIB and/or Group VIII metal componentsinto the support by impregnation, they are incorporated into thecatalyst by mixing an appropriate solid or liquid containing the desiredmetal with materials to be extruded through the die. Such a method mayprove less expensive and more convenient on a commercial scale than theimpregnation method.

Other known methods for depositing the Group VIB and Group VIII metalson the zeolite-containing support may be utilized. It is specificallynoted, however, that although the Group VIII metal may undergo some ionexchange with cations in the zeolite during preparation of the catalyst,it is preferred that at least some Group VIII metal be deposited on thesupport in locations other than the ion exchange sites of the zeolitecomponent. To ensure this result, the catalyst is preferably prepared tocontain more than the amount of Group VIII metal that would fully occupythe ion exchange sites of the zeolite component in the catalyst.

Although the two above-described catalysts are preferred for use in thehydrodewaxing reactor, other catalysts which will decrease the pourpoint of the reactor feed by selectively converting waxy paraffins tolower molecular weight hydrocarbons may be used. One such catalystcomprises a metallic hydrogenation component supported on a mixture of acrystalline aluminum phosphate and a porous refractory oxide asdescribed in U.S. Pat. No. 4,310,440, the disclosure of which is herebyincorporated by reference in its entirety. Examples of other catalystswhich may be used include metallic hydrogenation constituents depositedon mordenite, clinoptilolite, or low-potassium erionite. It will beunderstood that, although all of the hydrodewaxing catalysts describedabove contain at least one metallic hydrogenation component, thepresence of such a component is not necessary and the support withoutthe hydrogenation component may be used as the hydrodewaxing catalyst.

It has been found that the above-discussed hydrodewaxing catalysts tendto crack straight chain paraffins preferentially to slightly branchedparaffins. This high selectivity results in the effluent from thehydrodewaxing reactor having a higher than desired pour point. Attemptsto reduce the pour point further by operating the hydrodewaxing reactorat more severe conditions is undesirable because a substantialproportion of lube oil constituents, i.e., those components of thefeedstock which boil above about 650° F., is converted to lowermolecular weight hydrocarbons, thereby resulting in a loss of thedesired product. It has now been found that this undesirable loss oflube oil constituents can be avoided while obtaining a further reductionin pour point by contacting the effluent from the hydrodewaxing zonewith molecular hydrogen in the presence of a hydrocracking catalystunder conditions such that the overall conversion of 650° F. +components to components boiling at or below 650° F. in thehydrodewaxing and the hydrocracking steps combined is no more than about20 percent by volume, preferably no more than about 10 percent byvolume.

In accordance with the invention, the entire effluent from thehydrodewaxing reactor, which may include ammonia, hydrogen sulfide andlower molecular weight hydrocarbons, is passed to a hydrocrackingreactor where it is contacted with a hydrocracking catalyst in thepresence of molecular hydrogen. The contacting is normally accomplishedby passing the hydrodewaxing reactor effluent downwardly through thehydrocracking catalyst in a suitable reactor vessel under conditions ofelevated temperature and pressure. The temperature in the hydrocrackingreactor is normally maintained between about 500° F. and about 850° F.,preferably between about 600° F. and about 800° F. The pressure in thereactor is normally between about 500 p.s.i.g and about 3,000 p.s.i.g,preferably between about 1,500 p.s.i.g and about 2,500 p.s.i.g. Theliquid hourly space velocity of the feed through the hydrocrackingreactor is normally maintained between about 0.3 and about 8.0,preferably between about 0.5 and about 3.0. Hydrogen is passed throughthe reactor at a rate of about 8,000 standard cubic feet per barrel offeedstock, preferably between about 1,500 and about 10,000 standardcubic feet per barrel.

The catalyst used in the hydrocracking reactor promotes reactions thatresult in a further reduction in the pour point of the reactor feedunder the above described conditions without the overall conversion inthe hydrodewaxing and hydrocracking reactors combined being more thanabout 20 volume percent, preferably no more than about 10 volumepercent, of the constituents in the feed boiling above about 650° F. tocomponents boiling at or below 650° F. Normally, such catalysts will beuseful for producing middle distillates from heavy gas oils. Examples ofsuch catalysts are disclosed in detail in U.S. Pat. Nos. 4,097,365 and4,419,271, the disclosures of which are hereby incorporated by referencein their entirety. The catalyst described in U.S. Pat. No. 4,097,365 isa midbarrel hydrocracking catalyst comprising hydrogenation componentson a refractory oxide support comprising silica-alumina dispersed in amatrix of gamma alumina. The catalyst described in U.S. Pat. No.4,419,271 is an improvement of the previous catalyst in which acrystalline aluminosilicate zeolite having cracking activity, such ashydrogen Y-zeolite or a rare earth-exchanged Y-zeolite, is included inthe support. The hydrogenation components in both catalysts are themetals, oxides and sulfides of the Group VIII and/or the Group VIBelements. The most suitable hydrogenation components are selected fromthe group consisting of the metals, oxides and sulfides of platinum,palladium, cobalt, nickel, tungsten and molybdenum. Preferably, at leastone Group VIII metal component and at least one Group VIB metalcomponent are utilized, with the preferred combination being a nickeland/or cobalt component with a molybdenum and/or tungsten component.

The hydrogenation component or components are intimately composited on abase support comprising a mixture of a heterogeneous dispersion offinely divided silica-alumina in a matrix of alumina, preferably gammaalumina. The catalyst of U.S. Pat. No. 4,419,271 also contains, inintimate mixture with the dispersion, a suitable zeolite havingcatalytic activity for cracking hydrocarbons. These zeolites includenaturally occuring and synthetic crystalline aluminosilicates such asfaujasite, mordenite, erionite, Zeolite Y, Zeolite X, Zeolite L, ZeoliteOmega, Zeolite ZSM-4 and their modifications. These and other suchzeolitic molecular sieves are known to have activity for crackinghydrocarbons when a substantial portion of their ion exchange sites areoccupied with hydrogen ions or multivalent metal-containing cationsparticularly rare earth cations. A preferred zeolite for use in thesupport is a Y zeolite that has been ion-exchanged with ammonium ionsand then steam-stabilized in accordance with the procedure set forth inU.S. Pat. No. 3,929,672, the disclosure of which is hereby incorporatedby reference in its entirety. The most preferred zeolite for use in thesupport is a material known as LZ-10, a zeolitic molecular sieveavailable from Union Carbide, Linde Division. LZ-10 is a modified Yzeolite having a silica-to-alumina ratio between about 3.5 and about4.0, a surface area between about 500 and about 700 m² /gram, a unitcell size between about 24.25 and 24.35 Angstroms, a water adsorptioncapacity less than about 8 percent by weight, preferably less than about5 percent by weight, of the zeolite, and an ion-exchange capacity lessthan 20 percent of that of a sodium Y zeolite of comparablesilica-to-alumina ratio.

A large portion of the effluent from the hydrocracking reactor will beliquids boiling in the range between about 650° F. and about 1000° F.that are substantially free of waxy paraffinic hydrocarbons andtherefore will have a relatively low pour point. This fraction having alow pour point is a high quality lube stock and may be recovered fromthe hydrocracking zone effluent by passing the effluent to afractionating tower where the lube oil constituents are separated fromthe lower boiling constituents. The lube oil constituents can then beblended with other lube oil stocks to produce a lube oil of desiredcharacteristics. The lower boiling materials are recovered and may beused as desired.

In the embodiment of the invention described above, the entire effluentfrom the hydrotreating zone is passed to the hydrodewaxing zone and theentire effluent from the hydrodewaxing zone is passed to thehydrocracking zone. It will be understood that the process of theinvention is not limited to this particular flow scheme. For example, itmay be desirable to remove ammonia, hydrogen sulfide and gaseoushydrocarbons from the effluent of the hydrotreating zone, thehydrodewaxing zone or both. It may also be advisable in some instancesto distill the effluent from either zone or both zones to remove liquidhydrocarbons boiling below about 650° F. Although in the embodiment ofthe invention described above, the effluent from the hydrotreating zoneis passed into a separate hydrodewaxing reactor and then to a separatehydrocracking reactor, it will be understood that these two reactors canbe combined into one vessel containing two beds of different catalystsarranged such that the effluent from the hydrotreating zone would firstpass through the hydrodewaxing catalyst bed and then through thehydrocracking catalyst bed. This embodiment of the invention wouldeliminate the need for a second reactor vessel.

Although this invention has been primarily described in conjunction witha preferred embodiment thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart in the light of the foregoing description. Accordingly, it isintended to embrace within the invention all such variations,modifications and alternatives as are within the spirit and scope of theappended claims.

I claim:
 1. A process for converting a waxy hydrocarbon feedstockcontaining a substantial proportion of hydrocarbonaceous materialboiling above about 650° F. into a high quality lube oil stock whichcomprises:(a) contacting said waxy hydrocarbon feedstock with a dewaxingcatalyst in a dewaxing zone under conditions such that the pour point ofsaid feedstock is reduced, said dewaxing catalyst comprising a molecularsieve containing pores defined by 10-membered rings of oxygen atoms; (b)contacting the effluent from said dewaxing zone with molecular hydrogenin the presence of a hydrocracking catalyst in a hydrocracking zoneunder conditions such that a further reduction in pour point iseffected, wherein said contacting in steps (a) and (b) is such that theoverall conversion of components boiling above about 650° F. tocomponents boiling at or below about 650° F. is no more than about 20volume percent; and (c) recovering a high quality lube oil stock fromthe effluent of said hydrocracking zone.
 2. A process as defined byclaim 1 wherein said waxy hydrocarbon feedstock comprises a dearsenatedshale oil which has been hydrotreated to remove organonitrogen andorganosulfur components.
 3. A process as defined by claim 1 wherein saiddewaxing catalyst comprises a mixture of a porous refractory oxide and acrystalline silica polymorph.
 4. A process as defined by claim 3 whereinat least one hydrogenation component selected from the group consistingof Group VIB metal components and Group VIII metal components issupported on said mixture.
 5. A process as defined by claim 4 wherein aGroup VIB metal hydrogenation component and a Group VIII metalhydrogenation component are supported on said mixture.
 6. A process asdefined by claim 5 wherein said Group VIB metal hydrogenation componentcomprises a tungsten component or a molybdenum component and said GroupVIII metal hydrogenation component comprises a nickel component or acobalt component.
 7. A process as defined by claim 3 wherein said porousrefractory oxide comprises alumina.
 8. A process as defined by claim 3wherein said silica polymorph comprises silicalite.
 9. A process asdefined by claim 1 wherein said hydrocracking catalyst comprises atleast one hydrogenation component selected from the group consisting ofGroup VIB metal components and Group VIII metal components on arefractory oxide support comprising silica-alumina dispersed in a matrixof gamma alumina.
 10. A process as defined by claim 9 wherein saidhydrocracking catalyst contains a Group VIB metal hydrogenationcomponent and a Group VIII metal hydrogenation component
 11. A processas defined by claim 10 wherein said Group VIB metal hydrogenationcomponent comprises a tungsten component or molybdenum component andsaid Group VIII metal hydrogenation component comprises a nickelcomponent or cobalt component.
 12. A process as defined by claim 1wherein said dewaxing catalyst comprises an intimate mixture of a porousrefractory oxide and a crystalline zeolite having a ZSM-5 structurezeolite.
 13. A process as defined by claim 12 wherein at least onehydrogenation component selected from the group consisting of Group VIBmetal components and Group VIII metal components is supported on saidintimate mixture.
 14. A process as defined by claim 12 wherein saidzeolite having a ZSM-5 zeolite structure is selected from a groupconsisting of ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35 and ZSM-38.
 15. Aprocess as defined by claim 13 wherein a Group VIB metal hydrogenationcomponent and a Group VIII metal hydrogenation component are supportedon said intimate mixture.
 16. A process as defined by claim 15 whereinsaid Group VIB metal hydrogenation component comprises a tungstencomponent or molybdenum component and said Group VIII metalhydrogenation component comprises a nickel component or cobaltcomponent.
 17. A process as defined by claim 1 wherein said dewaxingzone and said hydrocracking zone are maintained in the same reactor. 18.A process as defined by claim 1 wherein the effluent from saidhydrodewaxing zone is treated to remove liquids boiling below about 650°F., ammonia, hydrogen sulfide and light hydrocarbon gases, and theremaining portion of said effluent is passed to said hydrocracking zone.19. A process as defined by claim 1 wherein said overall conversion ofcomponents boiling above about 650° F. to components boiling at or belowabout 650° F. is no more than about 10 percent by volume.
 20. A processas defined by claim 1 wherein said dewaxing catalyst comprises a mixtureof a porous refractory oxide and a crystalline aluminum phosphate.
 21. Aprocess as defined by claim 1 wherein said waxy hydrocarbon feedstock iscontacted with said dewaxing catalyst in the presence of molecularhydrogen.
 22. A process as defined by claim 1 wherein substantially allof the effluent from said dewaxing zone is contacted with molecularhydrogen in the presence of said hydrocracking catalyst in saidhydrocracking zone.
 23. A process for converting a waxy hydrocarbonfeedstock into a high quality lube oil stock which comprises:(a)contacting said waxy hydrocarbon feedstock with molecular hydrogen inthe presence of a hydrotreating catalyst in a hydrotreating zone underconditions such that the concentration of organosulfur andorganonitrogen components is reduced; (b) contacting the effluent fromsaid hydrotreating zone with molecular hydrogen in the presence of ahydrodewaxing catalyst in a hydrodewaxing zone under conditions suchthat the pour point of the hydrotreated feedstock from step (a) isreduced, wherein said hydrodewaxing catalyst comprises at least onehydrogenation component selected from the group consisting of a GroupVIB metal component and a Group VIII metal component on a supportselected from the group consisting of (1) a mixture of a porousrefractory oxide and a crystalline silica polymorph and (2) a mixture ofa porous refractory oxide and a crystalline zeolite having ZSM-5 zeolitestructure. (c) contacting the effluent from said hydrodewaxing zone withmolecular hydrogen in the presence of a hydrocracking catalyst in ahydrocracking zone under conditions such that a further reduction inpour point is effected, wherein said hydrocracking catalyst comprises atleast one hydrogenation component selected from the group consisting ofa Group VIB metal component and a Group VIII metal component on asupport comprising silica-alumina dispersed in a matrix of gammaalumina; and (d) recovering a high quality lube oil stock from theeffluent of said hydrocracking zone.
 24. A process as defined by claim23 wherein said hydrotreating catalyst comprises a Group VIB metalcomponent and Group VIII metal component on a refractory oxide support.25. A process as defined by claim 23 wherein the effluent from saidhydrotreating zone is treated to remove liquids boiling below about 650°F., ammonia, hydrogen sulfide, and light hydrocarbon gases, and theremaining portion of said effluent is passed to said hydrodewaxing zone.26. A process as defined by claim 23 wherein the effluent from saidhydrodewaxing zone is treated to remove liquidds boiling below about650° F., ammonia, hydrogen sulfide, and light hydrocarbon gases, and theremaining portion of said effluent is passed to said hydrocracking zone.27. A process for converting a waxy hydrocarbon feedstock containing asubstantial proportion of hydrocarbonaceous material boiling above about650° F. into a high quality lube oil stock which comprises:(a)contacting said waxy hydrocarbon feedstock with a dewaxing catalyst in adewaxing zone under conditions such that an effluent having a pour pointbelow the pour point of said feedstock is produced, said dewaxingcatalyst comprising a molecular sieve containing pores defined by10-membered rings of oxygen atoms; (b) using at least a portion of saideffluent from said dewaxing zone as at least a portion of the feedstockto a hydrocracking zone by passing said effluent to said hydrocrackingzone; (c) contacting said hydrocracking zone feedstock with molecularhydrogen in the presence of a hydrocracking catalyst in saidhydrocracking zone under conditions such that the pour point of saidhydrocracking zone feedstock is reduced, wherein said contacting insteps (a) and (c) is such that the overall conversion of componentsboiling above about 650° F. to components boiling at or below 650° F. ismore than about 20 volume percent and wherein said hydrocracking zonefeedstock has a final boiling point equal to or lower than the finalboiling point of said waxy hydrocarbon feedstock; and (d) recovering ahigh quality lube oil stock from the effluent of said hydrocrackingzone.
 28. A process as defined by claim 27 wherein said waxy hydrocarbonfeedstock is contacted with said dewaxing catalyst in the presence ofmolecular hydrogen.
 29. A process as defined by claim 27 wherein saidwaxy hydrocarbon feedstock comprises a dearsenated shale oil which hasbeen hydrotreated to remove organonitrogen and organosulfur components.30. A process as defined by claim 27 wherein said dewaxing catalystcomprises a mixture of a porous refractory oxide and a crystallinesilica polymorph.
 31. A process as defined by claim 30 wherein saidcrystalline silica polymorph comprises silicalite.
 32. A process asdefined by claim 27 wherein said hydrocracking catalyst comprises atleast one hydrogenation component selected from the group consisting ofGroup VIB metal components and Group VIII metal components on arefractory oxide support comprising silica-alumina dispersed in a matrixof gamma alumina.
 33. A process as defined by claim 32 wherein saidhydrocracking catalyst contains a Group VIB metal hydrogenationcomponent and a Group VIII metal hydrogenation component.
 34. A processas defined by claim 27 wherein said dewaxing catalyst comprises a porousrefractory oxide and a crystalline zeolite having a ZSM-5 zeolitestructure.
 35. A process as defined by claim 27 wherein the effluentfrom said dewaxing zone is treated to remove liquids boiling below about650° F. prior to passing said effluent to said hydrocracking zone.
 36. Aprocess as defined by claim 27 wherein the effluent from said dewaxingzone is treated to remove ammonia, hydrogen sulfide and lighthydrocarbon gases prior to passing said effluent to said hydrocrackingzone.